1. Field of the Invention
The present invention relates to processes and facilities for the automated treatment of municipal solid waste (MSW) (land-filled or obtained directly from the municipality), sewage sludge, and scrap tires to remove and reclaim any usable materials and for producing commercial lactic acid.
2. Related Art
Generally, solid waste materials and waste sludge are disposed of by land fill and/or incineration. Environmental restrictions on both land fills and incinerators demand that an alternative solid waste solution be implemented. The public outcry concerning pollution caused by incinerators has halted construction of many new incinerator projects. The government, as a reaction to the problems associated with land fills, has mandated that recycling be employed to conserve natural resources and arrest the flow of solid waste materials into land fills.
A number of technologies have been developed to recover recyclable materials from solid waste, to produce fuel, and to produce commercially useful substances. For example:
U.S. Pat. No. 5,198,074 discloses a process to produce ethanol from bamboo which involves chipping, shredding and washing of the bamboo, pressing to remove the water. The fiber is then prehydrolyzed with steam to give dissolved sugars and fermented to give ethanol.
U.S. Pat. No. 5,184,780 discloses a system for treating solid waste having one or more treatment lines for processing the solid waste to recover recyclable materials such as corrugated paper, ferrous metals, plastic products, paper and glass.
U.S. Pat. No. 5,135,861 discloses ethanol production from biomass which is hydrolyzed using the carbon dioxide produced from the fermentation reaction or the naturally occurring organic acids from citrus wastes as a catalyst.
U.S. Pat. No. 5,104,419 discloses a method of producing methanol from solid waste, for example, municipal solid waste, by partially oxidizing and combusting solid waste material, conducting the combustion gases, oxygen and carbon dioxide through the solid waste material, separating the less volatile components of the gas from the more volatile components, and reacting the more volatile components with carbon dioxide to form methanol.
U.S. Pat. No. 5,060,871 discloses methods of separating metal alloy particles by utilizing the difference in particle size, density and/or electric conductivity.
U.S. Pat. No. 5,036,005 discloses a method for the continuous fermentation production of fuel grade ethanol from a sugar, where the ethanol is removed in a solvent extraction column containing a solvent which is non-toxic to the fermentation microorganisms.
U.S. Pat. No. 5,009,672 discloses a process for the recycling and recovery of urban solid waste components by high pressure compression and screening as well as magnetic separation steps. The recovered putrescible organic component is then subjected to a process of anaerobic fermentation to give a biogas which can be used directly for the production of electric power.
U.S. Pat. No. 4,974,781 discloses a paper and plastic separation process which subjects the materials to moisture and heat to repulp the paper. The repulped materials are then separated from the non-pulpable materials and are then recycled, combusted or used as a feedstock in a chemical process.
U.S. Pat. No. 4,952,503 discloses a process for the continuous production of ethanol using a centrifugal separation step to remove the yeast.
U.S. Pat. No. 4,874,134 discloses a process for treating solid waste to recover recyclable materials such as corrugated paper, ferrous metals, non-ferrous metals, plastic products, paper and glass containers, as well as biodegradable waste materials which may be processed to give a compost. The bulky valuables, non-processable materials and redeemable materials are first recovered, a first ferrous metal fraction is then separated magnetically, the waste material is then shredded, a second ferrous metal fraction is then separated magnetically, and the paper fraction is then separated pneumatically to give a biodegradable fraction which can then be composted.
U.S. Pat. No. 4,692,167 discloses an apparatus for processing solid wastes for the production of a granule solid fuel by grinding, magnetically separating ferrous metals, screening, drying, gravity separation, cyclone separation, screening and press granulating.
U.S. Pat. No. 4,650,689 discloses a process for the preparation of ethanol from cellulosic materials by subjecting the cellulosic materials to a highly concentrated mineral acid gas such as HCl under pressure, and treatment with hot water to give a wort containing sugars which can be fermented.
U.S. Pat. No. 4,612,286 discloses a method for the acid hydrolysis of biomass having fermentable materials in a countercurrent diffusion treatment structure. Preferably, the acid is about 2 to 10% by volume sulfuric acid.
U.S. Pat. No. 4,553,977 discloses a method for separating solid waste components with a first trommel screen which removes aluminum cans to give an organics-rich fraction from which recyclable fiber products may be separated. Steel cans are removed by magnetic separation. The organics are isolated for use as a fuel, with or without pulping to recover paper pulp.
U.S. Pat. No. 4,541,530 discloses a method for separating metallic particles from non-metallic particles of processed solid waste by homogenizing and magnetically treating components of the waste to give a metallic concentrate, for example, an aluminum concentrate.
U.S. Pat. No. 4,384,897 discloses a method for treating biomass material by a two stage hydrolysis treatment, wherein in the first stage, the more easily hydrolyzed polysaccharides are depolymerized and in the second stage, the more difficultly depolymerizable polysaccharides are depolymerized. The biomass material may be subjected to a sensitization step between the first and the second hydrolysis stages by contact with molecular oxygen. The acids are neutralized with a base such as calcium carbonate or hydroxide to give a solution which is suitable for fermentation to give ethanol.
U.S. Pat. No. 4,341,353 discloses a method of recovering fuel and recyclables from refuse using disk screens and air classifiers.
U.S. Pat. No. 4,288,550 discloses a method of digesting garbage by anaerobic fermentation in the presence of ethanol producing yeast to directly convert starch to ethanol without a hydrolysis pretreatment and thereafter subjecting the product to methane producing anaerobic fermentation to give methane.
U.S. Pat. No. 4,069,145 discloses a method for separating particles of greater electrical conductivity from particles of lesser electrical conductivity in an electromagnetic eddy current separator apparatus.
U.S. Pat. No. 4,063,903 discloses an apparatus for the disposal of solid wastes by recovering the inorganic components and converting the organic component to a fuel or a fuel supplement. The shredded material is treated with an acid which is heated and dried and ground to give a finely divided fuel product.
Lactic acid, which occurs naturally in many foods, is used as a preservative to inhibit microbial spoilage in processed meats, seafoods, mayonnaise and salad dressings; as a raw material to produce emulsifiers such as fatty-acid lactylates and esters of mono-and di-glycerides used in bakery products, fillings and toppings; and as a flavor enhancer in soft drinks, margarine, jams, jellies, candies, wine and beer. Pharmaceutical applications include intravenous and dialysis solutions. About 40 million lbs. of lactic acid, much of it imported, are consumed annually in the United States.
Recently, lactic acid production has received attention because of the development of polylactic acid (PLA) plastics, which are 100% degradable and have been approved for use by the Food and Drug Administration (U.S. Department of Energy, Innovations for Tomorrow, National Renewable Energy Laboratory, Golden, Colo. (1992), pp. 1-2). PLA plastics can emulate the characteristics of many of the thermoplastics now used in packaging consumer goods and may become the basis of a family of environmentally benign polymers (Lipinsky, E. S. et al., Chem. Engin. Progresses 8:26 (1986)).
The major lactic acid-producing bacteria include the following genera: Streptococcus, Pediococcus, Leuconostoc, and Lactobacillus (Murray, R. G. E., Bergey's Manual of Determinative Bacteriology, Vol. 2, Sneath, P. H. A., ed., Williams and Wilkins, Baltimore, Md. (1986), p. 1209). Moreover, the major lactic acid producing Lactobacillus species include, Lactobacillus arabinosus, Lactobacillus pentosus, Lactobacillus plantarum, Lactobacillus xylosus, Lactobacillus delbrueckii, Lactobacillus bulgaricus, Lactobacillus casei and Lactobacillus leichmannii (McCaskey, T. A. et al., Appl. Biochem. Biotech. 45-46:555 (1994)).